package org.apache.lucene.document;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;

/**
 * Provides support for converting dates to strings and vice-versa.
 * The strings are structured so that lexicographic sorting orders 
 * them by date, which makes them suitable for use as field values 
 * and search terms.
 * 
 * <P>This class also helps you to limit the resolution of your dates. Do not
 * save dates with a finer resolution than you really need, as then
 * RangeQuery and PrefixQuery will require more memory and become slower.
 * 
 * <P>Compared to {@link DateField} the strings generated by the methods
 * in this class take slightly more space, unless your selected resolution
 * is set to <code>Resolution.DAY</code> or lower.
 */
public class DateTools {

    private final static TimeZone GMT = TimeZone.getTimeZone("GMT");

    private DateTools() {
    }

    /**
     * Converts a Date to a string suitable for indexing.
     * 
     * @param date the date to be converted
     * @param resolution the desired resolution, see
     *  {@link #round(Date, DateTools.Resolution)}
     * @return a string in format <code>yyyyMMddHHmmssSSS</code> or shorter,
     *  depeding on <code>resolution</code>; using UTC as timezone 
     */
    public static String dateToString(Date date, Resolution resolution) {
        return timeToString(date.getTime(), resolution);
    }

    /**
     * Converts a millisecond time to a string suitable for indexing.
     * 
     * @param time the date expressed as milliseconds since January 1, 1970, 00:00:00 GMT
     * @param resolution the desired resolution, see
     *  {@link #round(long, DateTools.Resolution)}
     * @return a string in format <code>yyyyMMddHHmmssSSS</code> or shorter,
     *  depeding on <code>resolution</code>; using UTC as timezone
     */
    public static String timeToString(long time, Resolution resolution) {
        Calendar cal = Calendar.getInstance(GMT);

        //protected in JDK's prior to 1.4
        //cal.setTimeInMillis(round(time, resolution));

        cal.setTime(new Date(round(time, resolution)));

        SimpleDateFormat sdf = new SimpleDateFormat();
        sdf.setTimeZone(GMT);
        String pattern = null;
        if (resolution == Resolution.YEAR) {
            pattern = "yyyy";
        } else if (resolution == Resolution.MONTH) {
            pattern = "yyyyMM";
        } else if (resolution == Resolution.DAY) {
            pattern = "yyyyMMdd";
        } else if (resolution == Resolution.HOUR) {
            pattern = "yyyyMMddHH";
        } else if (resolution == Resolution.MINUTE) {
            pattern = "yyyyMMddHHmm";
        } else if (resolution == Resolution.SECOND) {
            pattern = "yyyyMMddHHmmss";
        } else if (resolution == Resolution.MILLISECOND) {
            pattern = "yyyyMMddHHmmssSSS";
        } else {
            throw new IllegalArgumentException("unknown resolution " + resolution);
        }
        sdf.applyPattern(pattern);
        return sdf.format(cal.getTime());
    }

    /**
     * Converts a string produced by <code>timeToString</code> or
     * <code>dateToString</code> back to a time, represented as the
     * number of milliseconds since January 1, 1970, 00:00:00 GMT.
     * 
     * @param dateString the date string to be converted
     * @return the number of milliseconds since January 1, 1970, 00:00:00 GMT
     * @throws ParseException if <code>dateString</code> is not in the 
     *  expected format 
     */
    public static long stringToTime(String dateString) throws ParseException {
        return stringToDate(dateString).getTime();
    }

    /**
     * Converts a string produced by <code>timeToString</code> or
     * <code>dateToString</code> back to a time, represented as a
     * Date object.
     * 
     * @param dateString the date string to be converted
     * @return the parsed time as a Date object 
     * @throws ParseException if <code>dateString</code> is not in the 
     *  expected format 
     */
    public static Date stringToDate(String dateString) throws ParseException {
        String pattern = null;
        if (dateString.length() == 4)
            pattern = "yyyy";
        else if (dateString.length() == 6)
            pattern = "yyyyMM";
        else if (dateString.length() == 8)
            pattern = "yyyyMMdd";
        else if (dateString.length() == 10)
            pattern = "yyyyMMddHH";
        else if (dateString.length() == 12)
            pattern = "yyyyMMddHHmm";
        else if (dateString.length() == 14)
            pattern = "yyyyMMddHHmmss";
        else if (dateString.length() == 17)
            pattern = "yyyyMMddHHmmssSSS";
        else
            throw new ParseException("Input is not valid date string: " + dateString, 0);
        SimpleDateFormat sdf = new SimpleDateFormat(pattern);
        sdf.setTimeZone(GMT);
        Date date = sdf.parse(dateString);
        return date;
    }

    /**
     * Limit a date's resolution. For example, the date <code>2004-09-21 13:50:11</code>
     * will be changed to <code>2004-09-01 00:00:00</code> when using
     * <code>Resolution.MONTH</code>. 
     * 
     * @param resolution The desired resolution of the date to be returned
     * @return the date with all values more precise than <code>resolution</code>
     *  set to 0 or 1
     */
    public static Date round(Date date, Resolution resolution) {
        return new Date(round(date.getTime(), resolution));
    }

    /**
     * Limit a date's resolution. For example, the date <code>1095767411000</code>
     * (which represents 2004-09-21 13:50:11) will be changed to 
     * <code>1093989600000</code> (2004-09-01 00:00:00) when using
     * <code>Resolution.MONTH</code>.
     * 
     * @param resolution The desired resolution of the date to be returned
     * @return the date with all values more precise than <code>resolution</code>
     *  set to 0 or 1, expressed as milliseconds since January 1, 1970, 00:00:00 GMT
     */
    public static long round(long time, Resolution resolution) {
        Calendar cal = Calendar.getInstance(GMT);

        // protected in JDK's prior to 1.4
        //cal.setTimeInMillis(time);

        cal.setTime(new Date(time));

        if (resolution == Resolution.YEAR) {
            cal.set(Calendar.MONTH, 0);
            cal.set(Calendar.DAY_OF_MONTH, 1);
            cal.set(Calendar.HOUR_OF_DAY, 0);
            cal.set(Calendar.MINUTE, 0);
            cal.set(Calendar.SECOND, 0);
            cal.set(Calendar.MILLISECOND, 0);
        } else if (resolution == Resolution.MONTH) {
            cal.set(Calendar.DAY_OF_MONTH, 1);
            cal.set(Calendar.HOUR_OF_DAY, 0);
            cal.set(Calendar.MINUTE, 0);
            cal.set(Calendar.SECOND, 0);
            cal.set(Calendar.MILLISECOND, 0);
        } else if (resolution == Resolution.DAY) {
            cal.set(Calendar.HOUR_OF_DAY, 0);
            cal.set(Calendar.MINUTE, 0);
            cal.set(Calendar.SECOND, 0);
            cal.set(Calendar.MILLISECOND, 0);
        } else if (resolution == Resolution.HOUR) {
            cal.set(Calendar.MINUTE, 0);
            cal.set(Calendar.SECOND, 0);
            cal.set(Calendar.MILLISECOND, 0);
        } else if (resolution == Resolution.MINUTE) {
            cal.set(Calendar.SECOND, 0);
            cal.set(Calendar.MILLISECOND, 0);
        } else if (resolution == Resolution.SECOND) {
            cal.set(Calendar.MILLISECOND, 0);
        } else if (resolution == Resolution.MILLISECOND) {
            // don't cut off anything
        } else {
            throw new IllegalArgumentException("unknown resolution " + resolution);
        }
        return cal.getTime().getTime();
    }

    /** Specifies the time granularity. */
    public static class Resolution {

        public static final Resolution YEAR = new Resolution("year");
        public static final Resolution MONTH = new Resolution("month");
        public static final Resolution DAY = new Resolution("day");
        public static final Resolution HOUR = new Resolution("hour");
        public static final Resolution MINUTE = new Resolution("minute");
        public static final Resolution SECOND = new Resolution("second");
        public static final Resolution MILLISECOND = new Resolution("millisecond");

        private String resolution;

        private Resolution() {
        }

        private Resolution(String resolution) {
            this.resolution = resolution;
        }

        public String toString() {
            return resolution;
        }

    }

}
